Wet spinning non-circular polyacrylonitrile fibers by utilizing circular orifices and sequential coagulation

ABSTRACT

A METHOD OF PRODUCING SYNTHETIC FIBERS HAVING TOUGH OUTER SKINS AND DOG-BONE OR OTHER NON-CIRCULAR CROSSSECTIONS WHICH COMPRISES SPINNING SAID FIBER AND SUBJECTING THE SPUN FIBER TO SEQUENTIAL COAGULATION TREATMENTS WHEREBY THE OUTER CORE IS COAGULATED AND SHRINKS TO A TOUGH SHELL, SURROUNDING THE INNER CORE WHICH IS INCOMPLETELY COAGULATED AND COLLAPSED. THE FIBERS MAY BE USED IN CONVENTIONAL TEXTILE MATERIALS.

. S. TZENTIS Dec. 19, 1972 L WET SPINNING NON-CIRCULAR POLYACRYLONITRILEFIBERS BY UTILIZING CIRCULAR ORIFICES AND SEQUENTIAL COAGULATION FiledAug. 19, 1969 5 Sheets-Sheet l FIGS INVENTOR L. S. TZENTIS ATTORNEYSDec. 19, 5, E I 3,706,828

WET SPINNING NON-CIRCULAR POLYACHYLONITRILE FIBERS BY UTILIZING CIRCULARORIFICES AND SEQUENTIAL COAGULATION Filed Aug. 19. 1969 5 Sheets-Sheet 2INVENTOR L. S. TZENTI S BY 6% 2x52 M ATTORNEYS Dec. 19, 1972 L. S.TZENTIS WET SPINNING NON-CIRCULAR POLYACRYLONITRILE FIBERS BY UTILIZINGCIRCULAR ORIFICES AND SEQUENTIAL COAGULA'I'ION Filed Aug. 19. 1969 5Sheets-Sheet 3 FIG.8

INVENTOR L. S. TZEN TI S ATTORNEYS United States Patent 3,706,828 WETSPINNING NON-CIRCULAR POLYACRYLO- NITRILE FIBERS BY UTILIZING CIRCULARORIFICES AND SEQUENTIAL COAGULATION Leonidas S. Tzentis, Zurich,Switzerland, assignor to Dow Badische Company, Williamsburg, Va. FiledAug. 19, 1969, Ser. No. 851,368 Int. Cl. D01f 7/02 US. Cl. 264-182 10Claims ABSTRACT OF THE DISCLOSURE A method of producing synthetic fibershaving tough outer skins and dog-bone or other non-circularcrosssections which comprises spinning said fiber and subjecting thespun fiber to sequential coagulation treatments whereby the outer coreis coagulated and shrinks to a tough shell, surrounding the inner corewhich is incompletely coagulated and collapsed. The fibers may be usedin conventional textile materials.

This invention relates to synthetic fibers, particularly topolyacrylonitrile homopolymers, copolymers, or terpolymers in fibrousform. More specifically, the invention relates to a method of producingsuch fibers of noncircular cross-section.

The production of synthetic filaments has been the subject ofconsiderable inquiry since these fibers have been found to beparticularly susceptible to treatment with coloring materials such asdyes, flame retardants, anti-static materials, etc., while retainingstructural stability and flexibility when used in textiles.

Non-circular filaments have generally been prepared by melt spinning apolymeric material using a complicated spinnerette or by dry spinning.Typically, the spinnerettes are provided with orifices adapted tosuitably mold the fiber. Additionally, laminating techniques have beenused wherein shaped orifices separately extrude sections of the fiberwhich are laminated while still in a flowable condition prior tocoagulation. These spinnerettes are bulky and expensive and it is,therefore, desirable to devise a process adapted for use withconventional circular hole spinnerettes.

It has now been discovered that wet spun non-circular synthetic fibers,particularly acrylonitrile fibers, can be produced having irregularshapes and collapsed cores by a sequential coagulation treatmentconducted under such conditions as to produce a strong skin and weakcollapsible core.

With respect to acrylonitrile fibers, irregular shapes have beenproduced by such methods as solution spinning from organic solvents intoan aqueous coagulation bath as disclosed in 3,180,845 and 3,088,188 orsolution spinning from nitric acid into a coagulation bath containingnitric acid as disclosed in US. 2,907,096. The former methods requirecollapsing the voids which form while the latter must avoid the collapseof the voids. These patents do not allow controlled production ofnon-circular crosssection fibers.

The use of certain coagulating baths is undesirable in treatingsynthetic fibers since it is found to detract from the physicalproperties of the ultimate fibers, such as the flexibility andextensibility. Additionally, the conditions under which coagulationoccurs are found to produce variable characteristics in the fibers sothat a coagulating bath which works satisfactorily under some conditionsis unsatisfactory when those conditions are varied. This inventionprovides treatments which give useful fibers having the requisitestrength.

It is, therefore, a primary object of this invention to Patented Dec.19, 1972 provide a method which is adapted to produce synthetic polymerfibers having a non-circular cross-section by extruding from circularorifices.

A further object is to produce the subject fibers having improvedproperties, particularly increased cover in yarns and fabrics.

These and other objects and advantages of the invention will be apparentfrom a consideration of the following drawings and description. In thedrawings, FIGS. 17 are photomicrographs showing cross-section of fibersproduced by the present invention;

FIG. 8 is a schematic diagram illustrating a process for producing thefibers of FIGS. l-7.

The method of the present invention may be described generally ascomprising the steps of wet-spinning polymeric acrylonitrile materialfrom an aqueous medium containing an inorganic salt or from an organicmedium through orifices of circular cross-section, passing the filamentinto a mild first coagulation bath containing a solvent or saltcorresponding to the solvent or salt present in the spinning dope, whichbath contains 35-95% coagulant and is maintained at a temperature of 20to +25 C., preferably about 15 C., for a residence time of 1-12 seconds,optionally stretching the fibers therein, passing the initiallycoagulated fiber into a harsh second coagulation bath containing a likesolvent or salt in an amount of less than 35%, preferably less than 15%,which bath is maintained at a temperature of 30120 C., preferably 35-100C., for an average residence time of 20-75 seconds, washing, stretching,and drying. Fibers thus produced have a dense inner core which isintegrally bound to a relatively tough skin producing non-circularcross-section fibers.

Reference to FIG. 8 shows a schematic flow diagram wherein spin dope 3is extruded initially to produce fibers 6 which are spun from aspinnerette 1 through a first bath 2 wherein first coagulation bath 4 isprovided. The fibers 6 are removed from the bath across adjustableroller 8 onto a series of rolls 10 adapted to maintain tension on thefibers into second bath 12 containing heating coil 14 and secondcoagulation bath 16. Following this treatment, the fibers are washed intank 18 wherein guide rolls 20 keep the fibers submerged in wash liquid22, generally comprising water. After washing, a cold stretchingtreatment is provided by passing over movable rolls 24 and then a hotstretching treatment is provided using a boiling liquid such as watermaintained in tank 26. Finally, the fibers are dried in an oven (notshown). These steps are conventional in producing fibers and thoseskilled in the are will be aware of variations of this treatment whichmay be utilized depending upon the particular polymer being treated. Forexample, the stretching operations can be modified to provide more thanone cold stretching operation and/or more than one hot stretchingoperation. Likewise, the washing treatment may occur in more than onestage.

More specifically, the process of this invention comprises spinning asolution or dispersion of an acrylonitrile containing polymer through acircular hole spinnerette. The term acrylonitrile polymer as used inthis invention includes homopolymers, copolymers, and interpolymers ofacrylonitrile wherein the acrylonitrile is present in the polymer in aquantity of approximately by weight or more. Suitable comonomers forpreparation of copolymers useful in this invention include vinylmonomers such as acrylic and methacrylic acid esters, particularly thelower alkyl esters; other suitable vinyl compounds are vinyl acetate,vinyl chloride, vinyl bromide, and vinyl pyridine, and sulfo-containingvinyl compounds such as ethylene sulfonic acid, mineral salts thereof,sulfoethyl acrylate or methacrylate compounds and salts thereof. Ad-

ditional comonomers and methods of preparation will be apparent to thoseskilled in the art.

While acrylonitrile polymers are preferred, other polymers can be usedprovided the rate of coagulation is slow enough to allow a two-stagetreatment. Likewise, the fibers can be formed by blending theacrylonitrile polymer with minor (2-5%) proportions of compatiblepolymers, e.g. polyethylene glycol or different acrylonitrile polymers.Spinning dope is formed by dissolving the polymer in a suitable carrier,e.g., an aqueous solution carrier containing an inorganic salt or anorganic solvent, or both or by solution polymerizing the monomers in thespinning solvent. An aqueous zinc chloride solution may be utilized.Other aqueous saline solutions, that is, solutions containing anionizable salt, may be used, which contain mixed inorganic salts such aszinc chloride, sodium chloride, calcium chloride, magnesium chloride,etc. Generally, any

highly water-soluble salt may be utilized and this further includes thealkali metal thiocyanates, alkali earth metal thiocyanates, ammoniumthiocyanate, guanidine thiocyanate, lithium bromide, lithium iodide,sodium iodide. The aforementioned systems may be termed inorganicsolutions;" however, the invention should be understood to includeorganic spinning dopes wherein the polymer is dissolved in, or formed bysolution polymerization in, e.g., dimethyl acetamide or other organicspinning liquids. Mixed organic and inorganic systems may-be usedwherein the solvent system consists essentially of water containing atleast one water-miscible, aliphatic liquid containing one alcoholichydroxyl group and not more than six carbon atoms in the molecule, andat least one highly water-soluble salt as described above. For example,a system which has been used with satisfactory results comprises 48%zinc chloride, 28% water, and 24% methyl alcohol (weight percents areused). These and other systems are adequately described in the art asexemplified by US. Pats. 2,648,646 and 3,284,555.

The coagulation baths comprise a coagulation medium, generally water,and an organic solvent such as dimethyl acetamide or inorganic saltssuch as zinc chloride, or mixed organic-inorganic solutions containingwater, alcohol, and inorganic salt. The specific bath depends upon thespinning dope and generally the bath should contain ingredientscorresponding to those in the spinning dope. Naturally the compositionsand temperatures will vary.

In the first coagulation bath, relatively mild coagulation conditionsare used, e.g., the temperature is maintained at -20 to +25 C.,preferably l to 15 C.,

. and the spun fibers are allowed a dwell time of 1-12 seconds,preferably 5-10 seconds. When the bath comprises an aqueous inorganicsystem, the inorganic salt or mixture of salts should be present in aweight quantity of 20- 50%, preferably 25-45%, giving from 50-80%coagulant. When a mixed inorganic-organic system of an organic system isused, the organic component should :be present in a quantity of 5-60%,giving 40-90% coagulant. In the first coagulation bath, rapidcoagulation of the outer skin only is desirable and, therefore, tensionand temperature extremes should be avoided since these tend to increasethe rate of complete coagulation of the fibers. Thus, the lowtemperatures and the tension should be maintained throughout the fibertravel through the first bath.

When the fibers are introduced in the second bath, the outer skin willalready be coagulated; however, the dwell time and condition in thefirst bath will have been insufiicient to allow migration of thecoagulation medium to the inner core of the fiber. Thus, the inner corewill remain soft and uncoagulated. In the second bath, it is desirableto substantially increase the migration of coagulating mediums to theinner portion of the core. To accomplish this purpose, high temperaturesand concentrations of coagulant are utilized in a coagulating bathhaving greater proportion of coagulant than the first bath. For example,the second bath should contain (in organic system pp m t y H072 oi h gic med um and in inorganic systems, approximately 0-35% of the inorganicsalt. The temperature in the second bath should be maintained at 30-120C., preferably about 50 C. It is generally unnecessary to apply tensionto fibers in the second bath since high temperature accomplishessufiicient coagulation to yield the desired bistructured fibers. A dwelltime in the second bath should be maintained at approximately 20-75seconds, preferably 35-40 seconds, which will depend upon the exactconditions and ingredients used. This time is generally more than usedin the first bath.

While excessive stretching should generally be avoided in thecoagulation baths, it is possible and sometimes desirable to applytension in and between the baths and after the second baths. Thus, forexample, a stretch may be applied to the fibers in the first bath at aratio of 1- 6:1, between the first and second baths, up to a 3:1, ratio,and after the second bath, the fibers can be stretched at a 15:1 ratioor can be shrunk, depending upon the ultimate product desired. Thisstretching can be accomplished in a series of stretching steps byconventional techniques: for example, a three-stage stretch wherein astretch ratio of approximately 3:1 is applied in each step. Stretchingalso orients the fiber molecules and increases the strength of thefibers in coagulated fibers. A stretch ratio of 1:1 indicates noelongation of fibers was produced and a ratio of less than 1:1 indicatesshrinkage.

Following the second bath, the fibers are washed to eliminate thecoagulating medium and any remaining solvent. Washing is generallyaccomplished in hot water at about 20-50 C. and can be a sequentialstage-like treatment or a one-bath treatment.

The weak inner core of the fibers can be collapsed by the stretching anddrying steps. Essentially, the inner walls remain weak, while the outerskin is relatively tough due to the different rate of coagulation. Tocollapse the inner core and allow the skin to conform to the corecontours, the preliminary timed coagulations under specified conditionsare required. The fibers are dried in an oven, e.g., a hot air (-150 C.)type oven of conventionalconstruction.

The invention will be more fully understood by reference to thefollowing illustrative examples. In the examples, parts and percentagesare by weight unless otherwise indicated.

EXAMPLE 1 A homopolymer of acrylonitrile was spun from a zinc chloridesolution through a 30-hole spinnerette having circular holes 15 mils indiameter into a first coagulation bath containing a 41% zinc chlorideaqueous solution maintained at 15 C. The spinnerette pressure drop was20 p.s.i.g., and the polymer temperature issuing from the spinnerettewas 35 C. While passing through the first bath, a 5.86:1 stretch ratiowas applied by conventional adjustable driven rollers and the fiberswere lead to a second bath maintained at 30 C. and containing 41% zincchloride aqueous solution. The residence time in the first bath wasapproximately 8.4 seconds, while in the second bath, the residence timewas about 35 seconds. The fibers were washed at 30 C. and were removedfrom the wash bath and subjected to a 2-stage stretching operation, thefirst stage being on cold rollers at a ratio of 1.621, the second beingon hot rollers (80 C.) at a ratio of 7.5 :1. Following the stretching,the fibers were passed through an oven wherein hot air at approximatelyC. was blown over the fibers until dry. The dried fibers produced across-section corresponding to the photomicrograph of FIG. 1 wherein thecores and skin shrink. The fibers were 14 denier, and upon subjection tothe conventional testing techniques, the elongation was 47%, the yieldstrength was 1.09 grams per denier, the tenacity was 3.4 grams perdenier, and the elastic modulus was 36. On looping, 14.6 denier fiberstenacity measured 2.1, and elongation 22%. The luster was measured as62,8 and an average shape index of L30 was measured.

EXAMPLE 2 The procedure of Example 1 was repeated using a terpolymer ofacrylonitrile comprising 80% acrylonitrile and 20% of a mixture ofmethyl acrylate and methyl methacrylate. The fibers were stretched inthe first bath at a ratio of 3.75:1 and after the second bath in a 2-stage treatment comprising one cold (1:1) and one hot (16.8: 1) stretch.The residence time in the first bath was about 7 seconds and in thesecond bath was about 36- seconds. The fibers produced are shown in FIG.2 and were 14.5 denier with an elongation of 4%, tenacity of 4.1grams/denier, a yield strength of 1.1-8 grams/denier, and an elasticmodulus of 42. Upon looping, 14.9 denier fibers measured tenacity 3.2,and elongation 28%. The luster was measured as 57.7 and a shape index of1.52 was measured.

EXAMPLE 3 Procedure of Example 2 was repeated using a 12 mil -60-holespinnerette with the temperature in the first bath being 14.9 C. andZnCl concentration of 40.1%. The stretches after the second bath werecold (1.8:1) and hot (6.611). This produced the fibers shown in FIG. 3which are 14.1 denier with an elongation of 29%, a tenacity of 2.8grams/denier, a yield strength of 1.0 gram/ denier, and an elasticmodulus of 36. When looped, 13.6 denier fibers had tenacity 1.8, andelongation 17%. The luster was 64 and an average shape index was 1.40.

EXAMPLE 4 The procedure of Example 2 was repeated using a 60 mil 60-holespinnerette, a first bath temperature of 8 C., a concentration of 32%, astretch ratio of 1.82:1, and a residence time in the first bath of about5 seconds. In the second bath, the residence time was about 36 seconds,the wash bath temperature was at 44 C., and the hot stretch ratio was:1. The fibers produced are seen in FIG. 4 and were 18.3 denier withtenacity of 4.0 grams/denier, elongation of 42%, yield strength of 0.98,and elastic modulus of 39. When looped, the tenacity was 1.9 andelongation was 22%. The shape index was between 1.45 and 1.65.

EXAMPLE 5 The procedure of Example 4 was repeated using a 6 mil 60-holespinnerette, a first bath stretch of 30:1, and temperature of 9 C. Thehot stretch ratio after the second bath was 4.0:]. The fibers werepassed through boiling water before washing at 50 C. The fibers producedare shown in photomicrograph of FIG. 5, and were 28.7 denier with anelongation of 66%, a tenacity of 1.8 grams/denier, a yield strength of0.94 gram/denier, an dan elastic modulus of 26. When looped, theelongation was 27% and the tenacity was 1.3 grams/denier. The shapeindex was between 1.25 and 1.4.

EXAMPLE 6 The procedure of Example 5 was repeated using a first bathtemperature of 6.5 C. and stretch of 2.0. The stretch ratios after thesecond bath were cold (1:1), and not (10:1). The wash was at 31 C. Thisproduced the fibers shown in FIG. 6 which were 57.9 denier with anelongation of 38%, a tenacity of 2.1 grams/denier, a yield strength of1.0 gram/denier, and an elastic modulus of 34. When looped, the tenacitywas 1.3 grams/ denier, and the elongation 18%. The shape index wasbetween 1.5 and 1.7.

EXAMPLE 7 The procedure of Example -6 was repeated using a 65- holespinnerette and a first bath temperature of 0 C. The stretch ratiosafter the second bath were cold (2:1) and hot (7.8:1), respectively. Thefibers produced are shown in FIG. 7. They were 72.2 denier with atenacity of 1.6 grams/denier, elongation of 40%, yield strength of 0.88,and elastic modulus of 28. When looped, the tenacity was 0.33 andelongation was 24%. The shape index was between 1.25 and 1.45.

EXAMPLE 8 An acrylonitrile homopolymer dissolved to 10% solids in a5060% aqueous sodium thiocyanate solution was spun through a spinnerettehaving 15 holes of 8 mil diameter wherein a pressure drop of 10 p.s.i.g.occurs. These fibers were led into a first bath containing 10% sodiumthiocyanate and maintained at 5 C. for a dwell time of 7.8 seconds. Thefibers were not stretched therein. The second bath contained 22% sodiumthiocyanate maintained at 30 C. and the fibers dwell time was 36seconds. Following the second bath, the fibers were washed at 30 C., andhot stretched at a ratio of 12:1. After stretching, the fibers wereconducted to an oven wherein air at 125 C. was blown across the fibersuntil dried. The fibers produced were 20 denier/filament and correspondin structure to those shown in FIG. 1.

\EXAMPLE 9 An acrylonitrile copolymer containing a combination of methylacrylate and methyl methacrylate in a total quantity of less than 20%was dissolved to 25% solids in dimethyl acetamide. This solution wasspun through a spinnerette having 15 holes of 8 mil diameter into afirst bath containing 55% dimethyl acetamide maintained at 10 C. for adwell time of 5.15 seconds. The fibers were conducted without stretchingto a second bath containing 20% dimethyl acetamide maintained at 30 'C.for a residence time of 36 seconds. The fibers were then washed at 30 C.and were hot stretched at 8:1 ratio and then dried at an oventemperature of C. to produce 23.5 denier/filament having structurecorresponding to that shown in FIG. 2.

EXAMPLE 10 An acrylonitrile homopolymer dissolved in dimethyl sulfoxideto 25% solids was spun through a spinnerette having fifteen 8-mi1 holesinto a first bath containing 50% dimethyl sulfoxide maintained at 20 C.for a dwell time of 11.3 seconds. The fibers were conducted to a secondbath containing boiling water for a residence time of 36 seconds. Thefibers were then washed at 30 (1., hot stretched at an 8:1 ratio, andthen dried at 125 C. to yield 30 denier/filament, corresponding instructure to those of FIG. 1.

EXAMPLE 11 The procedure of Example 10 was repeated, substitutingdimethyl formarnide for the dimethyl sulfoxide and using dwell times inthe first bath of 7.9 seconds, and in the second bath of 7.2 secondswith 50% dimethyl formamide in the first bath and 0% in the second bath.A hot stretch ratio of 8:1 was used after the second bath. The fiberswere 60 denier/filament and corresponded to those of FIG. 1.

EXAMPLE 12 A spinning solution is prepared using 15% of a copolymercontaining 90% acrylonitrile and 10% methyl acrylate (M.W. about100,000) and dissolved in a solution consisting of 35% sodiumthiocyanate dissolved in 65% of a mixture of 20 parts water and 80 partsmethyl alcohol.

Fibers produced by this invention are highl flexible and show improvedstrength for non-circular fibers. They are useful in all lengths and inall diameters although diameters beyond the initial range of 3.350.0mils are difiicult to coagulate properly.

As an effective means of determining the non-circular shape of theultimate fibers a shape index is calculated as follows:

(Cross Sectional Perimeter) As can be seen if the fiber is round, theshape index is 1.0. The fibers of this invention preferably exhibit ashape index between 1.25 and 1.65, however, it is readily appreciatedthat widely varied shape indices can be produced and the preferred rangemerely designates those presently preferred.

The other testing procedures used in the examples are conventional inthe art and are available from such publications as Encyclopedia ofPolymer Technology, (John Wiley & Sons-1960), or from the AmericanSociety for Testing and Materials and the American Association ofTextile Chemists and Colorists.

Having described the invention, what is desired to be protected is asfollows:

What is claimed is:

1. In the known process comprising solution spinning polyacrylonitrilehomopolymers or copolymers containing at least 80% by weightacrylonitrile and up to 20% by weight of one or more vinyl monomersthrough a round orifice into a first bath to superficially coagulate thefiber; passing the superficially coagulated fiber into a second bath;washing the fibers; stretching the fibers; and drying the fibers;wherein the spinning solution and said first and second baths allcontain a member selected from the group consisting of an aqueous salinesolvent, an aqueous saline solvent containing an aliphatic alcohol,dimethyl acetamide, dimethyl formamide, and dimethyl sulfoxide, theimprovement which comprises forming shaped fibers by spinning saidsolution into said first bath wherein the concentration of the selectedmember is maintained in an amount of 15 to 65% by weight in 85 to 35% byweight water and the temperature of said first bath is maintained at 20to +25 C. and maintaining the fiber in said first bath for from about 1to about 12 seconds and thereafter passing the superficially coagulatedfiber into said second bath wherein the concentration of the selectedmember is maintained in an amount less than 35 by weight in more than 65by weight water and the temperature of said second bath is maintained at30 to 120 C. and maintaining said fiber in said second bath from about20 to 75 seconds.

2. Method of claim 1 wherein the member is an aqueous saline solventcontaining an aliphatic alcohol.

3. Method of claim 1 wherein the polymer is an acrylonitrilehomopolymer.

4. Method of claim 1 wherein the member is dimethyl acetamide.

5. Method of claim 1 wherein the member is dimethyl formamide.

6. Method of claim 1 wherein the member is dimethyl sulfoxide.

7. Method of claim 1 wherein an aqueous saline solvent member is used.

8. Method of claim 7 wherein the member is an aqueous solution of ZnCl9. Method of claim 2 wherein the member is an aqueous solution of ZnClcontaining a lower alcohol.

10. The method of claim 1 wherein an acrylonitrile copolymer is usedwhich contains vinyl monomers in an amount less than 20% by weightselected from the group consisting of acrylic acid lower alkyl esters,methacrylic acid lower alkyl esters, vinyl acetate, vinyl chloride,vinyl bromide, vinyl pyridine, and sulfo-containing vinyl monomers.

' References Cited UNITED STATES PATENTS 2,972,511 2/ 1961 Bechtold264-182 3,402,235 9/1968 Henderson et al. 264-182 3,097,053 7/1963Kurioka et al. 264-182 3,147,322 9/ 1964 Fujisaki et al. 264-1823,491,179 1/ 1970 Chinai et al. 264-182 FOREIGN PATENTS 653,828 5/1963Italy 264-182 1,285,249 7/1960 France 264-182 1,367,083 6/ 1964 France264-182 PHILIP E. ANDERSON, Primary Examiner US. Cl. X.R.

161-177; 260-855 R; 264-177 F, 210 F

